26.11.2015

EXPERIMENTING!

Extracting the jewellery continues to go well with the bulk of the large pieces out now. We've made some nice discoveries as we've gone along which has been fun. A "small" soap bar shaped silver ingot for example turned out to merely be one end of a long cast bar. We've uncovered about 18cm so far with no end in sight. We've also found two new round ingots.

One issue we are dealing with now is our second gold-plated torque half. This presumably looked like a real gold one originally and has the same design with the two rings or buffers at the throat end. After two thousand damp years however the copper underlying the thin gold plating has corroded through the gold to leave it a patchy dark green. Hopefully, after the analytical work is finished, we will be able to remove this corrosion and restore it to its original appearance.

Our problem at the moment is that the gold plate is extremely fragile. With a previous gold plated object from the hoard we pulled off a small area of plating when we removed an adjacent coin and we were very worried that this might might happen again. One way to deal with this issue suggested by colleagues was to try removing the object and surrounding coins in one block and then treat them with formic acid to safely take it all apart. We looked at this but it turned out not to be practical for a few reasons. One was that the coins are not really bonded together strongly enough to allow this block lift. Also we would loose the ability to record the individual coin positions in the way we do with all the others. Finally this half torque is lying within a large curved silver ingot and on top of another round ingot. Doing any kind of block lift would therefore have required all these to be removed at one time which just wasn't practical.

The use of formic acid to remove the corrosion that bonds the overlying coins to the gold plate was a good idea however. The problem is that we didn't want to use it on the main hoard body where it might affect nearby organic samples or drain down into the centre. In the end I decided that we had to do it as we couldn't risk damaging the gold plate again. What we did in the end was allow that part of the hoard surface to dry out to some extent to stop the acid diffusing away. Also I used concentrated acid so that I could use the smallest amount of fluid possible. All of this was done with a portable carbon filter extract unit to remove the fumes. Using a small paint brush I carefully painted the areas where the torque touched the coins and we left it to sit for about thirty minutes, (see bald man paints hoard, above). There was no visual change during this time but when we removed the extract unit and then carefully pried the coins off one by one we found that we'd removed no plate at all, except for one tiny piece, which was a great result. There was also no formic acid smell at all by this stage so we know that we managed to remove the acid by evaporation within the hour. All of the coins we removed were rinsed in water and then bagged as usual.

One nice thing this morning was that one of our volunteers got to remove a piece. This was Vic Perron (aka the smug *********). He's been known as this ever since he spotted a bracelet poking out of the hoard which I insisted was just a coin. Despite how insufferable he's been ever since it seemed only fair to let him remove it.

There's loads of video of the jewellery removal on Twitter now so just follow Jersey Heritage to find it.